According to The Guardian, the documents are the first to detail the inner workings of the team that operated under the country's Ministry of Defence.

The Guardian reports:

"Thousands of pages of highly classified files document how officials in the Ministry of Defence were worried they would be accused by the public of not taking UFOs seriously enough, and how some thought there really could be someone out there. 'It was important to appreciate that what is scientific "fact" today may not be true tomorrow,' a defence intelligence officer warned in August 1993.

"He pointed out: 'It was only a few hundred years ago that 'scientists' believed that the Earth was the centre of the universe.' He added: 'It was generally agreed until early this century that the atom could not be split.'"

In a 1995 briefing by a UFO desk officer, he said the country needed to study UFO data as a matter of national security.

In the Archives' highlights document they write: "Under the heading 'possibilities' the author lists mass hallucinations, hoaxes, US Black Project aircraft, Russian or Chinese aircraft or Extra-Terrestrial visitors. He says there is no hard evidence for alien craft but says 'if the sightings are not of this earth then their purpose needs to be established as a matter of priority. There has been no apparently hostile intent and other possibilities are: a) military reconnaissance b) scientific c) tourism.'"

One detail of particular interest for us here is that Britain sought information from the United States about UFOs. The U.S. said they weren't interested. Again here's a bit from the Archives' highlights document (note we've hyperlinked to the large PDF files containing the pertinent record; and note that MoD stands for "Ministry of Defence"):

"DEFE 24/1985/1 (p239-40) contains a response by MoD to a US Air Force request for information on British UFO policy in 1965. MoD says 'our policy is to play down the subject and to avoid attaching undue attention to it', as a result there had never been any political pressure for an official study. In 1995, the UFO Desk asked RAF Air Attache in Washington to ascertain the US Department of Defense's line on UFOs.

"In file DEFE 24/1985/1 (p81-82) the response says 'after posing the questions to a variety of staff [in HQ US Space Command] and receiving blank stares in return' he was referred to the Department of Defense's website which said the US had no interest in UFO reports, a policy which was 'consistent with our own, but they discourage approaches from the public rather more politely than we do.'"

"Roswell

"DEFE 24/1985/1 (p10) in January 1997 a Defence Intelligence official responded to a question on briefings given to MoD by CIA on Roswell incident and reports of 'crashed UFOs' stating 'we have no data on the alleged "Roswell incident" or any UAP/UFO crashes in either the UK or US and have never, as far as we can tell from existing files, received any briefings from any US agencies, including the CIA.'"

The BBC reports that the special UFO unit existed between 1950 to 2009. The British government began releasing documents about the program in 2008.